/*
 * Copyright 2010 Francisco Modesto
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.googlecode.gwt.tinyaop.client;

/**
 * Intercepts calls on an interface on its way to the target. These are nested
 * "on top" of the target.<br>
 * The user should implement the invoke(Invocation) method to modify the
 * original behavior. E.g. the following class implements a tracing interceptor
 * (traces all the calls on the intercepted method(s)):
 * 
 * <pre>
 * class TracingInterceptor implements Interceptor {
 *   public Object invoke(Invocation i) {
 *     System.out.println("method " + i.getMethod().getName() + " is called on "
 *         + i.getThis() + " with args " + i.getArguments());
 *     Object ret = i.proceed();
 *     System.out.println("method " + i.getMethod() + " returns " + ret);
 *     return ret;
 *   }
 * }
 * </pre>
 * 
 * Implementation notes:<br>
 * Interceptors are instantiate using <code>new InterceptorClass()</code>
 * interceptors needs to provide a visible (to the class) default constructor.
 * </ul>
 */
public interface Interceptor {

  /**
   * Implement this method to perform extra treatments before and after the
   * invocation. Polite implementations would certainly like to invoke
   * {@link Invocation#proceed()}.
   * 
   * @param invocation the method invocation
   * @return the result of the invoked method
   */
  public Object invoke(Invocation invocation);
}
